Timeline: add preview of painted picture for Paint event

- enable "Capture picture" check-box in Timeline capture filter when
    Timeline on trace events experiment is enabled;
- add disabled-by-default-devtools.timeline.{picture,layers} categories
    to trace filter when the above is checked;
- associate recorded SkPicture with the last paint event of the layer
    with matching id;
- display pictures preview in Timeline's details view, when these are
    available.

BUG=

Review URL: https://codereview.chromium.org/328143003

git-svn-id: svn://svn.chromium.org/blink/trunk@176196 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Make ServiceWorker an ActiveDOMObject

Before this patch, the ServiceWorker object returned by
navigator.serviceWorker.register() could be garbage collected
prematurely causing state change event handlers to never be invoked.
This patch makes ServiceWorker an ActiveDOMObject and keeps it alive
until either stop() is called on it (indicating detach of the parent
document) or it reaches the terminal "deactivated" state (soon to be
renamed "redundant").

For future work, it may be possible to be more clever and allow the SW
to die when it has no event handlers.

BUG=383972

Review URL: https://codereview.chromium.org/330173003

git-svn-id: svn://svn.chromium.org/blink/trunk@176197 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: fix build after r176183

R=haraken@chromium.org
BUG=305497
NOTRY=true

Review URL: https://codereview.chromium.org/332183002

git-svn-id: svn://svn.chromium.org/blink/trunk@176198 bbb929c8-8fbe-4397-9dbb-9b2b20218538